Please, could you retag the question ? -> the vim tag is missing.
First, I'll want to remind you this thread (which was in a better forum IMO): http://meta.stackoverflow.com/questions/25925/vim-questions-so-or-su were a bigger majority than the number of people in favour of using SE/unix have already expressed themselves in favour of SO.
Now my opinion. I'm quite tired of this scattering of the vim community -- which I fail to see the point in this tag based world. One wants quality responses, it means the people knowing the tool have to follow 3 different sites (of course it would have been too simple to post directly were vim gurus live (its official mailing-list)).
As of today, we have 38 vim questions on SE/unix, 491 on SU, and 2799 on SO.
Must we abandon the other sites to use this seldom used site (regarding vim questions) ? Or must we continue where the knowledge has already proven to be ? If we must abandon a site, it would be best to migrate all questions from the site abandoned.
Now, of all the sites, this one is as appropriate as SO. Indeed the majority of vim questions (and answers) transcend OSes issues (they are platform agnostic, as programming questions are). So far, I have seen a little bit more vim questions in the context of vim being used for programming tasks than questions about vim being used on some very specific platform. Moreover, it's not rare that some seemingly innocent questions that could have fit on SU require vim scripting, (dare I say programming?) skills (I've seen this one today).
As a conclusion, I'd vote: stay were most questions already are -> SO